The present invention relates to methods of interpreting coded information carriers and to methods of processing the response of such carriers to an interrogating magnetic field.
In certain types of human and machine-readable information-bearing label, a set of elements is used to represent the information contained in the label. This representation may be made by varying the characteristics of the elements comprising the label, and also by the position in which the label elements are placed. Reading apparatus senses the characteristics and placement of the elements in order to decode the information contained within the label. The elements in the label are sequentially scanned, to discover the presence of the constituent elements and to measure their characteristics and position and thence to decode the information contained by the label.
This application describes label coding methods by which information represented on such a label can be decoded. Typical label embodiments are where the label is manufactured from a plurality of magnetically active elements supported on a substrate. Information is coded by controlling the relative positions. Independent control of the physical properties of the elements, such as shape may also be used.
In alternative embodiments, information may be coded by controlling the relative angles of orientation of the easy axis of the magnetic elements and in some cases element shape some other physical property can be independently controlled to further encode the information carrier.
In certain types of label decoding system a label consisting of a set of elements is scanned, that is the elements are activated in turn by applying a signal to which the scanned element responds, and to which the reading apparatus is sensitive. Either or both of the means of generating the scanning signal, and the means of generating the received Signal in the reading apparatus select a single elements in turn so that the signal from a particular element may be resolved from that of the other elements.
According to one aspect of the present invention there is provided a method of decoding an information carrier comprising a plurality of magnetic elements supported by, or incorporated in, a substrate, wherein the relative positions and/or physical dimensions of said magnetic elements represents the information encoded by said information carrier, the method comprising the steps of:
i) applying an interrogation signal to each of the elements of said information carrier;
ii) detecting the response of said magnetic elements to said interrogation signal;
iii) processing the response detected in ii) so as to determine an estimate of a mathematical function which defines the relative velocity between the interrogating signal and each of the magnetic elements, from which the relative positions and/or the relative physical dimensions can be determined.
Conveniently, detection of the magnetic response of said magnetic elements may comprise observation of harmonics which are generated by the magnetic element from an applied AC field as its magnetic state is altered by the interrogating magnetic field. The presence of a magnetic element and details of the physical dimensions of the magnetic element, can advantageously be identified in a plot of the detected amplitude of the harmonic signal. The presence of a set of signals in the otherwise quiescent detected signal indicates the issuance of harmonic signal by a magnetic element as its magnetic properties are active. The means of scanning may be automatic by electronically scanning the interrogating signal and the receive sensitivity along the label or by an automatic mechanism causing the label elements to be interrogated in turn. Alternatively the scanning may be manually operated where the label is moved past the reading apparatus by hand, or alternatively the reading apparatus or part thereof may be moved past the label by hand.
Information may be advantageously encoded into the label by varying either the length of the material elements, that is the size of the element normal to the longitudinal axis of the label, or the width of the elements. By maintaining the element width constant, variations in element length predominantly cause a change in amplitude of the received signal which can be detected in order to recognise additional coded information.